Skylon - AbsoluteAstronomy.com

Skylon is a design for an unpiloted spaceplane

Spaceplane

A spaceplane is a vehicle that operates as an aircraft in Earth's atmosphere, as well as a spacecraft when it is in space. It combines features of an aircraft and a spacecraft, which can be thought of as an aircraft that can endure and maneuver in the vacuum of space or likewise a spacecraft that...

by the British company Reaction Engines Limited

Reaction Engines Limited

Reaction Engines Limited is a British aerospace company based in Oxfordshire, England.- History & personnel :Reaction Engines was founded in 1989 by Alan Bond and Richard Varvill and John Scott-Scott...

(REL). It uses a combined-cycle, air-breathing rocket engine to reach orbit in a single stage. A fleet of vehicles is envisaged; the design is aiming for re-usability up to 200 times. In paper studies, the costs per kilogram of payload are hoped to be lowered from the current £15,000/kg to £650/kg , including the costs of research and development (R&D), with costs expected to fall much more over time after the initial expenditures have amortised. The cost of the programme has been estimated by the developer to be about $12 billion.

The vehicle design is for a hydrogen-powered aircraft that would take off from a conventional runway, and accelerate to Mach

Mach number

Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...

5.4 at 26 km using atmospheric air before switching the engines to use the internal liquid oxygen

Lox

Lox is salmon fillet that has been cured. In its most popular form, it is thinly sliced—less than in thickness—and, typically, served on a bagel, often with cream cheese, onion, tomato, cucumber and capers...

(LOX) supply to take it to orbit. It would then release its payload, which can weigh up to 15 tonnes, and re-enter the atmosphere. The payload would be carried in a standardised payload container or passenger compartment.

During re-entry the relatively light vehicle would fly back through the atmosphere and land back at the runway, with its skin protected by a ceramic

Ceramic

A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...

composite

Composite material

Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...

. It would then undergo inspection and any necessary maintenance and, if the design goal is achieved, be able to fly again within two days. , only a small portion of the funding required to develop and build Skylon has been secured. The research and development work on the SABRE engine design is proceeding under a small European Space Agency

European Space Agency

The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...

(ESA) grant. In January 2011, REL submitted a proposal to the British Government to request additional funding for the Skylon project. In April 2011, REL announced that they had secured $350 million of further funding contingent on a test of the engine's precooler technology being successful. Testing began in June 2011, and is expected to continue to the end of the year.

Research and development programme

Skylon is based upon a previous project of Alan Bond

Alan Bond (rocket developer)

Alan Bond is Managing Director of Reaction Engines Ltd and associated with Project Daedalus, Blue Streak missile, HOTOL, Reaction Engines Skylon and the Reaction Engines A2 hypersonic passenger aircraft.- Career :...

, which was known as HOTOL

HOTOL

HOTOL, for Horizontal Take-Off and Landing, was a British air-breathing space shuttle effort by Rolls Royce and British Aerospace.Designed as a single-stage-to-orbit reusable winged launch vehicle, it was to be fitted with a unique air-breathing engine, the RB545 called the Swallow, to be...

. The development programme of HOTOL began in 1982, a time when space technology was moving towards reusable launch system

Reusable launch system

A reusable launch system is a launch system which is capable of launching a launch vehicle into space more than once. This contrasts with expendable launch systems, where each launch vehicle is launched once and then discarded.No true orbital reusable launch system is currently in use. The...

s such as the American Space Shuttle

Space Shuttle

The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...

. In conjunction with British Aerospace

British Aerospace

British Aerospace plc was a UK aircraft, munitions and defence-systems manufacturer. Its head office was in the Warwick House in the Farnborough Aerospace Centre in Farnborough, Hampshire...

and Rolls Royce

Rolls-Royce plc

Rolls-Royce Group plc is a global power systems company headquartered in the City of Westminster, London, United Kingdom. It is the world’s second-largest maker of aircraft engines , and also has major businesses in the marine propulsion and energy sectors. Through its defence-related activities...

, a design emerged that proved highly promising, so much so that the British Government donated £2 million to further their work. However, in 1988, the Conservative government withdrew funding, and the development programme was terminated. Following this major setback, Alan Bond decided to set up his own company, Reaction Engines Limited

Reaction Engines Limited

, with the hope of continuing development with private funding.

After having secured funding, the design of the craft was revisited, undergoing a rigorous redesign throughout much of the 1990s. In the last decade, Reaction Engines has been working with the University of Bristol

University of Bristol

The University of Bristol is a public research university located in Bristol, United Kingdom. One of the so-called "red brick" universities, it received its Royal Charter in 1909, although its predecessor institution, University College, Bristol, had been in existence since 1876.The University is...

to develop the engines vital to the success of Skylon. The STRICT/STERN engines produced by this programme were deemed a great success. The next stage of development is to construct a full-sized working prototype of the SABRE Engine.

The differences between Skylon and its predecessor are numerous. For example, HOTOL was to have been launched from a rocket sled

Rocket sled

A rocket sled is a test platform that slides along a set of rails, propelled by rockets.As its name implies, a rocket sled does not use wheels. Instead, it has sliding pads, called "slippers", which are curved around the head of the rails to prevent the sled from flying off the track...

(to save weight), whereas Skylon uses a conventional retractable undercarriage

Undercarriage

The undercarriage or landing gear in aviation, is the structure that supports an aircraft on the ground and allows it to taxi, takeoff and land...

. Skylon also uses a different engine design; the SABRE engine is expected to offer higher performance. Another issue that the Skylon design aims to circumvent was the intrinsically poor stability of HOTOL. The weight of the rear-mounted engine would have tended to make the HOTOL vehicle flip over mid-flight due to the centre of mass lying behind the centre of drag. Attempts to fix this problem ended up sacrificing much of the potential payload that the HOTOL vehicle could carry, and contributed to the failure of the project. Skylon would solve this by placing the engines at the end of the wings closer to the centre of the vehicle and thus moving the centre of mass forward, ahead of the centre of drag

Drag (physics)

In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...

.

Request for funding from the British government was undertaken in 2000, with a proposal that could have offered a large potential return on investment. The request was not taken up at that time. Subsequent discussions with the British National Space Centre

British National Space Centre

The British National Space Centre was a British government body that coordinated civil space activities for the UK. It was replaced on 1 April 2010 by the UK Space Agency.-Structure:...

led to agreement in 2009 on a co-funding agreement between BNSC, ESA and REL to continue technology development for the SABRE engine.

In February 2009, the British National Space Centre

British National Space Centre

The British National Space Centre was a British government body that coordinated civil space activities for the UK. It was replaced on 1 April 2010 by the UK Space Agency.-Structure:...

(now the UK Space Agency

UK Space Agency

The UK Space Agency is a United Kingdom government agency responsible for its civil space programme. It was established on 1 April 2010 to replace the British National Space Centre and took over responsibility for government policy and key budgets for space and represents the UK in all negotiations...

) and ESA

European Space Agency

The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...

announced that they were partially funding work with €1 million Euros ($1.28 million dollars) on Skylon's engine to produce a demonstration engine by 2011.

The Technology Demonstration Programme will last approximately 2.5 years and will benefit from another €1 million from the ESA. This programme will take Reaction Engines Ltd from a Technology Readiness Level

Technology Readiness Level

Technology Readiness Level is a measure used by some United States government agencies and many of the world's major companies to assess the maturity of evolving technologies prior to incorporating that technology into a system or subsystem...

(TRL) of 2/3 up to 4/5. The former UK Minister for Science and Innovation in 2009, Lord Drayson

Paul Drayson, Baron Drayson

Paul Rudd Drayson, Baron Drayson PC is a British businessman, amateur racing driver and politician. He was Minister of Science in the Department for Business, Innovation and Skills until May 2010, where he replaced Ian Pearson. In June 2009 he was additionally appointed as Minister of State for...

, commented on Skylon in a speech: "This is an example of a British company developing world-beating technology with exciting consequences for the future of space."

As of 2010, the funding required to develop and build the entire craft has not yet been secured, and so current research and development work is focused on the engines, under an ESA grant of €1 million. In January 2011, REL submitted a proposal to the British Government requesting additional funding for the Skylon project.

On April 13, 2011, REL announced that the Skylon design had passed several rigorous independent reviews. On May 24, the ESA publicly declared the design to be feasible, having found "no impediments or critical items" in the proposal.

The next milestone will be a static test of the engine precooler in June, 2011. Testing of the SABRE engine will commence in June 2011 with the start of Phase 3 in the Skylon development programme. An REL spokesperson announced that they had secured $350 million of further funding, contingent on successful completion of the full-sized precooled jet engine test in June 2011.

Pre-orders are expected in the 2011–2013 time frame coinciding with the formation of the manufacturing consortium.

Technology and innovations

Structure of the fuselage

The fuselage

Fuselage

The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...

of Skylon is expected to be carbon fibre space frame

Space frame

A space frame or space structure is a truss-like, lightweight rigid structure constructed from interlocking struts in a geometric pattern. Space frames can be used to span large areas with few interior supports...

; a light and strong structure that supports the weight of the aluminium fuel tank

Fuel tank

A fuel tank is safe container for flammable fluids. Though any storage tank for fuel may be so called, the term is typically applied to part of an engine system in which the fuel is stored and propelled or released into an engine...

s and to which the ceramic skin

Skin (aircraft)

The wings and fuselage of aircraft are covered by what is referred to as the skin. Aircraft have a protective and functional covering that is also called the skin of the flying machines. Soft single skin kite examples the use of the term for kite wings....

is attached. Multiple layers of reflective foil thermal insulation

Thermal insulation

Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...

fill the spaces of the frame.

The currently proposed Skylon model C2 will be a physically large vehicle, with a length of 82 metres (269 ft) and a diameter of 6.3 metres (20.7 ft). Because it will use a low-density liquid hydrogen

Liquid hydrogen

Liquid hydrogen is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form.To exist as a liquid, H2 must be pressurized above and cooled below hydrogen's Critical point. However, for hydrogen to be in a full liquid state without boiling off, it needs to be...

fuel, a great volume is needed to contain enough energy to reach orbit. The propellant is intended to be kept at low pressure to minimise stress; a vehicle that is both large and light has an advantage during atmospheric reentry

Atmospheric reentry

Atmospheric entry is the movement of human-made or natural objects as they enter the atmosphere of a celestial body from outer space—in the case of Earth from an altitude above the Kármán Line,...

compared to other vehicles due to a low ballistic coefficient

Ballistic coefficient

In ballistics, the ballistic coefficient of a body is a measure of its ability to overcome air resistance in flight. It is inversely proportional to the negative acceleration—a high number indicates a low negative acceleration. BC is a function of mass, diameter, and drag coefficient...

.
Because of the low ballistic coefficient, Skylon would be slowed
at higher altitudes where the air is thinner. As a result, the skin of the vehicle would only reach 1100 Kelvin

Kelvin

The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

(K). In contrast, the smaller Space Shuttle

Space Shuttle

is heated to 2000 K on its leading edge

Leading edge

The leading edge is the part of the wing that first contacts the air; alternatively it is the foremost edge of an airfoil section. The first is an aerodynamic definition, the second a structural one....

, and so employs an extremely heat-resistant but extremely fragile silica thermal protection system

Space Shuttle thermal protection system

The Space Shuttle thermal protection system is the barrier that protects the Space Shuttle Orbiter during the searing heat of atmospheric reentry...

. The Skylon design need not use such a system, instead opting for using a far thinner yet durable reinforced ceramic skin. However, due to turbulent flow around the wings during re-entry, some parts of Skylon would need to be actively cooled.

Skylon would employ a highly loaded tightly spaced wheel assembly, to save weight and also interior space when the wheels are retracted into the fuselage

Fuselage

. Because this wheel design distributes the weight of the aircraft and the force of its landing over a smaller area of the runway, it would require a specially strengthened runway. It will possess a retractable undercarriage

Undercarriage

The undercarriage or landing gear in aviation, is the structure that supports an aircraft on the ground and allows it to taxi, takeoff and land...

with high pressure tires and water cooled brakes. If problems were to occur just before a take-off the brakes would be applied to stop the vehicle, the water boiling away to dissipate the heat. Upon a successful take-off, the water would be jettisoned, thus reducing the weight of the undercarriage by many tons. During landing, the empty vehicle would be far lighter, and hence the water would be unneeded. The payload fraction

Payload fraction

In aerospace engineering, payload fraction is a common term used to characterize the efficiency of a particular design. Payload fraction is calculated by dividing the weight of the payload by the weight of the otherwise empty aircraft when fully fueled...

would be significantly greater than normal rockets and the vehicle should be fully reusable (200 times or more).

SABRE Engines

One of the significant features of the Skylon design is the engine, called SABRE. The engines are designed to operate much like a conventional jet engine

Jet engine

A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...

at up to around Mach

Mach number

5.5 (1700 m/s), 26 kilometres (16 mi) altitude, beyond which the air inlet closes and the engine operates as a highly efficient rocket

Rocket

A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...

to orbital speed

Orbital speed

The orbital speed of a body, generally a planet, a natural satellite, an artificial satellite, or a multiple star, is the speed at which it orbits around the barycenter of a system, usually around a more massive body...

.
The proposed engine for the vehicle is not a scramjet

Scramjet

A scramjet is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow...

, but a jet engine running combined cycle

Combined cycle

In electric power generation a combined cycle is an assembly of heat engines that work in tandem off the same source of heat, converting it into mechanical energy, which in turn usually drives electrical generators...

s of a precooled jet engine, rocket engine

Rocket engine

A rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...

and ramjet

Ramjet

A ramjet, sometimes referred to as a stovepipe jet, or an athodyd, is a form of airbreathing jet engine using the engine's forward motion to compress incoming air, without a rotary compressor. Ramjets cannot produce thrust at zero airspeed and thus cannot move an aircraft from a standstill...

. Originally the key technology for this type of precooled jet engine did not exist as it required a heat exchanger that was ten times lighter than the state of the art. Research conducted since then has achieved the necessary performance.

Operating an air-breathing jet engine at up to Mach 5.5 is difficult. Several previous engines proposed by other designers have been good as jet engines but performed poorly as rockets. This engine design aims to be a good jet engine within the atmosphere, as well as being an excellent rocket engine outside. The problem with operating at Mach 5.5 has been that the air coming into the engine heats up as it is compressed into the engine, which can cause the engine to overheat. Attempts to avoid these issues typically make the engine much heavier (scramjet

Scramjet

A scramjet is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow...

s/ramjet

Ramjet

s) or greatly reduce the thrust (conventional turbojets/ramjets). In either case the end result is an engine that has a poor thrust to weight ratio

Thrust-to-weight ratio

Thrust-to-weight ratio is a ratio of thrust to weight of a rocket, jet engine, propeller engine, or a vehicle propelled by such an engine. It is a dimensionless quantity and is an indicator of the performance of the engine or vehicle....

at high speeds, resulting in an engine that is too heavy to assist much in reaching orbit.

The SABRE engine design aims to avoid this by using some of the liquid hydrogen

Liquid hydrogen

fuel to cool the air at the inlet. The air is then used for combustion much like in a conventional jet. Because the air is cooled at all speeds, the jet can be built of light alloy

Alloy

An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

s and the weight is roughly halved. Additionally, more fuel can be burnt at high speed. Beyond Mach 5.5, the air would still be unusably hot despite the cooling, so the air inlet closes and the engine relies solely on on-board liquid oxygen

Liquid oxygen

Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...

and hydrogen fuel as in a normal rocket.

Because the engine uses the atmosphere as reaction mass at low altitude, it will have a high specific impulse

Specific impulse

Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...

(around 2,800 seconds), and burn about one fifth of the propellant that would have been required by a conventional rocket. Therefore, it would be able to take off with much less total propellant than conventional systems. This, in turn, means that it does not need as much lift

Lift (force)

A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...

or thrust

Thrust

Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....

, which permits smaller engines, and allows conventional wings to be used. While in the atmosphere, using wings to counteract gravity drag

Gravity drag

In astrodynamics and rocketry, gravity drag is a measure of the loss in the net performance of a rocket while it is thrusting in a gravitational field...

is more fuel-efficient than simply expelling propellant (as in a rocket), again reducing the total amount of propellant needed.

"Single Stage to Orbit" capability

A vehicle that can fly to orbit without staging is known as single stage to orbit (SSTO). Proponents of SSTO claim that staging causes a number of problems such as being difficult, expensive or even impossible to recover, reuse and reassemble the parts and therefore believe that SSTO designs hold the promise of reducing the cost of space-flight.

The Skylon design aims to take off from its specially strengthened runway

Runway

According to ICAO a runway is a "defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft." Runways may be a man-made surface or a natural surface .- Orientation and dimensions :Runways are named by a number between 01 and 36, which is generally one tenth...

, fly into low earth orbit

Low Earth orbit

A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...

, re-enter the atmosphere

Atmospheric reentry

, and land back on its runway like a conventional aeroplane, without staging, while being fully reusable

Reusable launch system

Payload bay

The payload bay of the Skylon C2 design is a cylinder 13 metres (42.7 ft)
long and 4.8 metres (16 ft) in diameter. It is designed to be comparable with current payload dimensions, and yet able to support the containerisation of payloads that Reaction Engines hopes for in the future. To an equatorial orbit, Skylon could deliver 15 tonne to a 300 kilometres (186 mi) height or 11 tonne to a 800 kilometres (497 mi) altitude. Using interchangeable payload containers, Skylon could be fitted to carry satellites or fluid cargo into orbit, or, in a specialised habitation module, up to 30 astronaut

Astronaut

An astronaut or cosmonaut is a person trained by a human spaceflight program to command, pilot, or serve as a crew member of a spacecraft....

s in a single launch.

Economics and political will

The complete Skylon project has a projected R&D cost of over $10 billion and will continue for another 7–10 years.

Once operative, Skylon could potentially lower satellite costs from the current £15,000/kg to £650/kg, according to evidence submitted to the UK parliament by Reaction Engines Ltd. However, funding and support from the British government has not been easy to establish.

According to David Willetts

David Willetts

David Linsay Willetts is a British Conservative Party politician and the Minister of State for Universities and Science. He is the Member of Parliament representing the constituency of Havant in Hampshire.-Education:...

, the UK Minister of State for Universities and Science

Department for Business, Innovation and Skills

The Department for Business, Innovation and Skills is a ministerial department of the United Kingdom Government created on 5 June 2009 by the merger of the Department for Innovation, Universities and Skills and the Department for Business, Enterprise and Regulatory Reform .-Ministers:The BIS...

"The European Space Agency is funding proof of concept work for Skylon from UK contributions. This work is focusing on demonstrating the viability of the advanced British engine technology that would underpin the project. Initial work will be completed in mid 2011 and if the trial is successful, we will work with industry to consider next steps."

REL intend Skylon to be a fully for-profit commercial venture, with the aircraft being manufactured and sold to operators. REL themselves (as a small company) intend to manufacture the precooler, with the other parts of the aircraft being designed and built by aerospace manufacturers. According to Management Today, Skylon is sometimes discussed as a possible replacement for NASA

NASA

The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

's Space Shuttle

Space Shuttle

Engine technology test program

, hardware testing of the "heat exchanger technology crucial to [the] hybrid air- and liquid oxygen-breathing [Sabre] rocket motor" is under way. This is an important step in the Sabre development process, to demonstrate to investors that the technology is viable. Tests are scheduled to continue to December 2011.

The Sabre engine "relies on a heat exchanger capable of cooling incoming air to -140 C, to provide liquid oxygen (LOX) for mixing with hydrogen to provide jet thrust during atmospheric flight before switching to tanked LOX when in space." The autumn 2011 test programme will validate that the critical heat exchanger technology can perform as needed for the engine to obtain adequate oxygen from the atmosphere to support low-altitude, high-performance operation.

Specifications (Skylon C2)

Fuselage diameter: 6.75 m (22.15 ft)
Specific impulse
Specific impulse
Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...

: 3500 s (35 kN·s/kg) atmospheric, 450 s (4.5 kN·s/kg) exoatmospheric
SABRE engine thrust/weight ratio: up to 14 atmospheric

External links

Reaction Engines Limited
Mark Hempsell from REL on The Space Show talking about Skylon
World Tiles Skylon model
Liquid Air Cycle Engine (LACE) rocket equation reasonably well predicts the performance of Skylon

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Research and development programme

Technology and innovations

Structure of the fuselage

SABRE Engines

"Single Stage to Orbit" capability

Payload bay

Economics and political will

Engine technology test program

Specifications (Skylon C2)

See also

External links